Method and system for adaptive modulations and signal field for closed loop multiple input multiple output (MIMO) wireless local area network (WLAN) system

ABSTRACT

A method for communicating information is disclosed and includes, in a multiple-input-multiple-output (MIMO) communication system utilizing a plurality of modulation types and a plurality of spatial streams, determining an aggregate noise characteristic based upon a noise characteristic of each of the plurality of spatial streams. A receiver may be configured to receive subsequent data based on one or both of: a current modulation type for modulating a current spatial stream and at least one subsequent modulation type for modulating at least one subsequent spatial stream. The current modulation type and the at least one subsequent modulation type may be based on the determined aggregate noise characteristic. A constellation field may be encoded to uniquely identify a combination comprising the current modulation type, and the at least one subsequent modulation type.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

The present application is a continuation of application Ser. No.11/115,804, filed on Apr. 26, 2005, which is a continuation-in-part ofapplication Ser. No. 11/110,241, filed on Apr. 20, 2005, which claimspriority to provisional application No. 60/650,941 filed on Feb. 7,2005. This application also makes reference, claims priority to, andclaims the benefit of U.S. Provisional Application Ser. No. 60/656,357filed Feb. 25, 2005.

This application makes reference to:

U.S. patent application Ser. No. 11/061,567 filed Feb. 18, 2005;

U.S. patent application Ser. No. 11/052,389 filed Feb. 7, 2005; and

U.S. patent application Ser. No. 11/052,353 filed Feb. 7, 2005.

U.S. patent application Ser. No. 11/110,241 filed Apr. 20, 2005.

All of the above stated applications are hereby incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for an adaptive modulations and signal field for aclosed loop multiple input multiple output (MIMO) wireless local areanetwork (WLAN) system.

BACKGROUND OF THE INVENTION

The Institute for Electrical and Electronics Engineers (IEEE), inresolution IEEE 802.11, also referred as “802.11”, has defined aplurality of specifications which are related to wireless networking.With current existing 802.11 standards, such as 802.11(a), (b), (g),which can support up to 54 Mbps data rates, either in 2.4 GHz or in 5GHz frequency bands, the IEEE standards body created a new task group,802.11n, to support higher than 100 Mbps data rates. Among them arebeing discussed specifications for “closed loop” feedback mechanisms bywhich a receiving station may feed back information to a transmittingstation to assist the transmitting station in adapting signals, whichare sent to the receiving station.

In closed loop feedback systems, a transmitting station may utilizefeedback information from a receiving station to transmit subsequentsignals in what is called “beamforming”. Beamforming is a technique tosteer signals to a certain direction for the receiver to receive it morereliably with less noise and interference. Compounded with demands fornew features and capabilities, various proposals for new 802.11n basedfeedback mechanisms are emerging to address the demand for these newfeatures and capabilities. For example, there exists a demand for theintroduction of new capabilities, which may enable a receiving mobileterminal to feedback pertinent information to a transmitting mobileterminal. This feedback of pertinent information may enable thetransmitting mobile terminal to adapt its mode of transmission basedupon the feedback information provided by the receiving mobile terminal.As with any communication system, a major goal is to enable thetransmitting mobile station to achieve a higher information transferrate to the receiving mobile terminal, while simultaneously achieving alower packet error rate (PER). Notwithstanding, there are no existingmethodologies that adequately address these shortcomings and/or satisfythe demand for these new features and capabilities in WLANs.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for an adaptive modulations and signal field fora closed loop multiple input multiple output (MIMO) wireless local areanetwork (WLAN) system, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exemplary block diagram of a transceiver comprising atransmitter and a receiver in a MIMO system, which may be utilized inaccordance with an embodiment of the invention.

FIG. 2 a is an exemplary block diagram of communications circuitry thatmay be utilized in accordance with an embodiment of the invention.

FIG. 2 b is an exemplary block diagram of a transceiver comprisingtransmitter and a receiver with adaptive modulation/demodulation for aMIMO system, which may be utilized in accordance with an embodiment ofthe invention.

FIG. 3 is an exemplary block diagram of a transceiver comprising atransmitter and a receiver with adaptive modulation/demodulation andcoding/decoding for a MIMO system, which may be utilized in accordancewith an embodiment of the invention.

FIG. 4 shows an exemplary graph of throughput versus SNR simulations fora 2×2 system utilizing a 40 MHz D-type channel with perfect channelestimation based on MMSE-LE for packet size of 1000 bytes, in accordancewith an embodiment of the invention.

FIG. 5 shows an exemplary training sequence, which may be utilized inconnection with an embodiment of the invention.

FIG. 6 shows exemplary changes to the SIG-N field, in accordance with anembodiment of the invention.

FIG. 7 is a flowchart illustrating exemplary steps for closed loopmodulation type requested by a receiver, in accordance with anembodiment of the invention.

FIG. 8 is a flowchart illustrating exemplary steps for closed loopmodulation type determined by a transmitter based on channel feedbackfrom a receiver, in accordance with an embodiment of the invention.

FIG. 9 is a flowchart illustrating exemplary steps for open loopmodulation type determined by a transmitter, in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention relate to a method and system foran optional closed loop mechanism with adaptive modulations for amultiple input multiple output (MIMO) wireless local area network (WLAN)system. In accordance with an embodiment of the invention, a channelsounding mechanism may be utilized to communicate information between atransmitter and a receiver. Various embodiments of the invention mayutilize properties of Eigenvalue analysis of MIMO systems to reduce thenumber of bits of binary information required to encode a modulationtype among a plurality of modulation types to a spatial stream among aplurality of spatial streams. The reduction in the number of requiredbits in various embodiments of the invention compared to otherconventional approaches may enable greater flexibility in systems thatutilize closed loop feedback mechanisms. Various embodiments of theinvention may utilize a new channel sounding mechanism in a closed loopsystem that enables adaptive modulation and beamforming. Modulationtypes and coding rates may be chosen adaptively per-stream based onranges in the values of SNRs. The transmitter may choose modulationtypes and coding rates based on channel feedback information.

In accordance with an embodiment of the invention, with regard tochannel information, MIMO systems may utilize the channel moreefficiently based on observable criteria. In an example of observablecriteria, RF channels that are characterized by higher signal to noiseratios (SNR) may support higher data transfer rates than RF channelswith lower SNR. Eigenbeamforming, or “beamforming”, may be utilized withsystems that support the exchange of feedback information from areceiver to a transmitter (or “closed loop” systems) to “steer beams”which may enable signal energy to be focused in a desired direction. Anyof a plurality of RF channels which may be utilized by a transmitter tocommunicate with a receiver may be referred to as “downlink channels”,while any of a plurality of RF channels which may be utilized by areceiver to communicate with a transmitter may be referred to as “uplinkchannels”.

Adaptive modulation and coding rate techniques may be utilized withbeamforming techniques such that a plurality of signals, or “streams”,may be transmitted simultaneously that comprise different amounts ofdata. This technique may also be known as streamloading. The modulationand/or coding rate may be chosen per stream efficiently, with either orboth capable of being modified, based on channel information.

In one aspect of the invention, modulation and/or coding schemes may beselected on a per-stream basis to maximize the aggregate informationtransfer rate while minimizing packet error rates (PER) for informationtransmitted simultaneously via a plurality of RF channels. This mayentail evaluating the SNR performance of individual RF channels, andadapting the modulation and/or coding scheme for each RF channel basedon SNR, and data rate maximization criteria. Exemplary measures ofsignal quality may comprise, for example, SNR and PER.

FIG. 1 is an exemplary block diagram of transceiver comprising atransmitter and a receiver in a MIMO system, which may be utilized inaccordance with an embodiment of the invention. FIG. 1 shows transceivercomprising a transmitter 100, a receiver 101, a processor 140, abaseband processor 142, a plurality of transmitter antennas 115 a . . .115 n, and a plurality of receiver antennas 117 a . . . 117 n. Thetransmitter 100 may comprise a coding block 102, a puncture block 104,an interleaver block 106, a plurality of mapper blocks 108 a . . . 108n, a plurality of inverse fast Fourier transform (IFFT) blocks 110 a . .. 110 n, a beamforming V matrix block 112, and a plurality of digital toanalog (D to A) conversion and antenna front end blocks 114 a . . . 114n. The receiver 101 may comprise a plurality of antenna front end andanalog to digital (A to D) conversion blocks 116 a . . . 116 n, abeamforming U* matrix block 118, a plurality of fast Fourier transform(FFT) blocks 120 a . . . 120 n, a channel estimates block 122, anequalizer block 124, a plurality of demapper blocks 126 a . . . 126 n, adeinterleaver block 128, a depuncture block 130, and a Viterbi decoderblock 132.

The variables V and U* in beamforming blocks 112 and 118 respectivelyrefer to matrices utilized in the beamforming technique. U.S.application Ser. No. 11/052,389 filed Feb. 7, 2005, provides a detaileddescription of Eigenbeamforming, which is hereby incorporated herein byreference in its entirety.

The processor 140 may perform digital receiver and/or transmitterfunctions in accordance with applicable communications standards. Thesefunctions may comprise, but are not limited to, tasks performed at lowerlayers in a relevant protocol reference model. These tasks may furthercomprise the physical layer convergence procedure (PLCP), physicalmedium dependent (PMD) functions, and associated layer managementfunctions. The baseband processor 142 may similarly perform functions inaccordance with applicable communications standards. These functions maycomprise, but are not limited to, tasks related to analysis of datareceived via the receiver 101, and tasks related to generating data tobe transmitted via the transmitter 100. These tasks may further comprisemedium access control (MAC) layer functions as specified by pertinentstandards.

In the transmitter 100, the coding block 102 may transform receivedbinary input data blocks by applying a forward error correction (FEC)technique, for example, binary convolutional coding (BCC). Theapplication of FEC techniques, also known as “channel coding”, mayimprove the ability to successfully recover transmitted data at areceiver by appending redundant information to the input data prior totransmission via an RF channel. The ratio of the number of bits in thebinary input data block to the number of bits in the transformed datablock may be known as the “coding rate”. The coding rate may bespecified using the notation i_(b)/t_(b), where t_(b) represents thetotal number of bits that comprise a coding group of bits, while i_(b)represents the number of information bits that are contained in thegroup of bits t_(b). Any number of bits t_(b)−i_(b) may representredundant bits that may enable the receiver 101 to detect and correcterrors introduced during transmission. Increasing the number ofredundant bits may enable greater capabilities at the receiver to detectand correct errors in information bits. The penalty for this additionalerror detection and correction capability may result in a reduction inthe information transfer rates between the transmitter 100 and thereceiver 101. The invention is not limited to BCC, and any one of aplurality of coding techniques, for example, Turbo coding or low densityparity check (LDPC) coding, may also be utilized.

The puncture block 104 may receive transformed binary input data blocksfrom the coding block 102 and alter the coding rate by removingredundant bits from the received transformed binary input data blocks.For example, if the coding block 102 implemented a ½ coding rate, 4 bitsof data received from the coding block 102 may comprise 2 informationbits, and 2 redundant bits. By eliminating 1 of the redundant bits inthe group of 4 bits, the puncture block 104 may adapt the coding ratefrom ½ to ⅔. The interleaver block 106 may rearrange bits received in acoding rate-adapted data block from the puncture block 104 prior totransmission via an RF channel to reduce the probability ofuncorrectable corruption of data due to burst of errors, impactingcontiguous bits, during transmission via an RF channel. The output fromthe interleaver block 106 may also be divided into a plurality ofstreams where each stream may comprise a non-overlapping portion of thebits from the received coding rate-adapted data block. Therefore, for agiven number of bits in the coding rate-adapted data block, b_(db), agiven number of streams from the interleaver block 106, n_(st), and agiven number of bits assigned to an individual stream i by theinterleaver block 106, b_(st)(i):

$\begin{matrix}{b_{db} = {\sum\limits_{i = 0}^{n_{st} - 1}\;{b_{st}(i)}}} & {{equation}\mspace{14mu}\lbrack 1\rbrack}\end{matrix}$

For a given number of coded bits before interleaving, b_(db), each bitmay be denoted by an index, k=0, 1 . . . b_(db)−1. The interleaver block106 may assign bits to the first spatial stream, spatial stream 0,b_(st)(0), for bit indexes k=0, n_(st), 2*n_(st), . . . , b_(db)−n_(st).The interleaver block 106 may assign bits to spatial stream 1,b_(st)(1), for bit indexes k=1, n_(st)+1, 2*n_(st)+1, . . . ,b_(db)−n_(st)+1. The interleaver block 106 may assign bits to spatialstream 2, b_(st)(2), for bit indexes k=2, n_(st)+2, 2*n_(st)+2, . . . ,b_(db)−n_(st)+2. The interleaver block 106 may assign bits to spatialstream n_(st), b_(st)(n_(st)), for bit indexes k=n_(st)−1, 2*n_(st)−1,3*n_(st)−1, . . . , b_(db)−1.

The plurality of mapper blocks 108 a . . . 108 n may comprise a numberof individual mapper blocks that is equal to the number of individualstreams generated by the interleaver block 106. Each individual mapperblock 108 a . . . 108 n may receive a plurality of bits from acorresponding individual stream, mapping those bits into a “symbol” byapplying a modulation technique based on a “constellation” utilized totransform the plurality of bits into a signal level representing thesymbol. The representation of the symbol may be a complex quantitycomprising in-phase (I) and quadrature (Q) components. The mapper block108 a . . . 108 n for stream i may utilize a modulation technique to mapa plurality of bits, b_(st)(i), into a symbol.

The beamforming V matrix block 112 may apply the beamforming techniqueto the plurality of symbols, or “spatial modes”, generated from theplurality of mapper blocks 108 a . . . 108 n. The beamforming V matrixblock 112 may generate a plurality of signals where the number ofsignals generated may be equal to the number of transmitting antenna atthe transmitter 100. Each signal in the plurality of signals generatedby the beamforming V block 112 may comprise a weighted sum of at leastone of the received symbols from the mapper blocks 108 a . . . 108 n.

The plurality of IFFT blocks 110 a . . . 110 n may receive a pluralityof signals from the beamforming block 112. Each IFFT block 110 a . . .110 n may subdivide the bandwidth of the RF channel into a plurality ofn sub-band frequencies to implement orthogonal frequency divisionmultiplexing (OFDM), buffering a plurality of received signals equal tothe number of sub-bands. Each buffered signal may be modulated by acarrier signal whose frequency is based on that of one of the sub-bands.Each of the IFFT blocks 110 a . . . 110 n may then independently sumtheir respective buffered and modulated signals across the frequencysub-bands to perform an n-point IFFT thereby generating a composite OFDMsignal.

The plurality of digital (D) to analog (A) conversion and antenna frontend blocks 114 a . . . 114 n may receive the plurality of signalsgenerated by the plurality of IFFT blocks 110 a . . . 110 n. The digitalsignal representation received from each of the plurality of IFFT blocks110 a . . . 110 n may be converted to an analog RF signal that may beamplified and transmitted via an antenna. The plurality of D to Aconversion and antenna front end blocks 114 a . . . 114 n may be equalto the number of transmitting antenna 115 a . . . 115 n. Each D to Aconversion and antenna front end block 114 a . . . 114 n may receive oneof the plurality of signals from the beamforming V matrix block 112 andmay utilize an antenna 115 a . . . 115 n to transmit one RF signal viaan RF channel.

In the receiver 101, the plurality of antenna front end and A to Dconversion blocks 116 a . . . 116 n may receive analog RF signals via anantenna, converting the RF signal to baseband and generating a digitalequivalent of the received analog baseband signal. The digitalrepresentation may be a complex quantity comprising I and Q components.The number of antenna front end and A to D conversion blocks 116 a . . .116 n may be equal to the number of receiving antenna 117 a . . . 117 n.

The plurality of FFT blocks 120 a . . . 120 n may receive a plurality ofsignals from the plurality of antenna front end and A to D conversionblocks 116 a . . . 116 n. The plurality of FFT blocks 120 a . . . 120 nmay be equal to the number of antenna front end and A to D conversionblocks 116 a . . . 116 n. Each FFT block 120 a . . . 120 n may receive asignal from an antenna front end and A to D conversion block 116 a . . .116 n, independently applying an n-point FFT technique, and demodulatingthe signal by a utilizing a plurality of carrier signals based on the nsub-band frequencies utilized in the transmitter 100. The demodulatedsignals may be mathematically integrated over one sub band frequencyperiod by each of the plurality of FFT blocks 120 a . . . 120 n toextract n symbols contained in each of the plurality of OFDM signalsreceived by the receiver 101.

The beamforming U* block 118 may apply the beamforming technique to theplurality of signals received from the plurality of FFT blocks 120 a . .. 120 n. The beamforming U* block 118 may generate a plurality ofsignals where the number of signals generated may be equal to the numberof spatial streams utilized in generating the signals at the transmitter100. Each of the plurality of signals generated by the beamforming U*block 118 may comprise a weighted sum of at least one of the signalsreceived from the FFT blocks 120 a . . . 120 n.

The channel estimates block 122 may utilize preamble information,contained in a received RF signal, to compute channel estimates. Theequalizer block 124 may receive signals generated by the beamforming U*block 118. The equalizer block 124 may process the received signalsbased on input from the channel estimates block 122 to recover thesymbol originally generated by the transmitter 100. The equalizer block124 may comprise suitable logic, circuitry, and/or code that may beadapted to transform symbols received from the beamforming U* block 118to compensate for fading in the RF channel.

The plurality of demapper blocks 126 a . . . 126 n may receive symbolsfrom the equalizer block 124, reverse mapping each symbol to one or morebinary bits by applying a demodulation technique, based on themodulation technique utilized in generating the symbol at thetransmitter 100. The plurality of demapper blocks 126 a . . . 126 n maybe equal to the number of streams in the transmitter 100.

The deinterleaver block 128 may receive a plurality of bits from each ofthe demapper blocks 126 a . . . 126 n, rearranging the order of bitsamong the received plurality of bits. The deinterleaver block 128 mayrearrange the order of bits from the plurality of demapper blocks 126 a. . . 126 n in, for example, the reverse order of that utilized by theinterleaver 106 in the transmitter 100. The depuncture block 130 mayinsert “null” bits into the output data block received from thedeinterleaver block 128 that were removed by the puncture block 104. TheViterbi decoder block 132 may decode a depunctured output data block,applying a decoding technique that may recover the binary data blocksthat were input to the coding block 102.

In operation, the processor 140 may receive decoded data from theViterbi decoder 132. The processor 140 may communicate received data tothe baseband processor 142 for analysis and further processing. Theprocessor 140 may also communicate data received via the RF channel, bythe receiver 101, to the channel estimates block 122. This informationmay be utilized by the channel estimates block 122, in the receiver 101,to compute channel estimates for a received RF channel. The basebandprocessor 142 may generate data to be transmitted via an RF channel bythe transmitter 100. The baseband processor 142 may communicate the datato the processor 140. The processor 140 may generate a plurality of bitsthat are communicated to the coding block 102.

The elements shown in FIG. 1 may comprise components that may be presentin an exemplary embodiment of a wireless communications terminal. Oneexemplary embodiment of a may be a wireless communications transmittercomprising a transmitter 100, a processor 140, and a baseband processor142. Another exemplary embodiment of a may be a wireless communicationsreceiver comprising a receiver 101, a processor 140, and a basebandprocessor 142. Another exemplary embodiment of a may be a wirelesscommunications transceiver comprising a transmitter 100, a receiver 101,a processor 140, and a baseband processor 142.

FIG. 2 a is an exemplary block diagram of communications circuitry thatmay be utilized in accordance with an embodiment of the invention. Withreference to FIG. 2 a is shown a baseband processor 272, a transceiver274, an RF front end 280, a plurality of receive antennas 276 a, . . . ,276 n, and a plurality of transmitting antennas 278 a, . . . , 278 n.The transceiver 274 may comprise a processor 282, a receiver 284, and atransmitter 286.

The processor 282 may be adapted to perform digital receiver and/ortransmitter functions in accordance with applicable communicationsstandards. These functions may comprise, but are not limited to, tasksperformed at lower layers in a relevant protocol reference model. Thesetasks may further comprise the physical layer convergence procedure(PLCP), physical medium dependent (PMD) functions, and associated layermanagement functions. The baseband processor 272 may be adapted toperform functions in accordance with applicable communicationsstandards. These functions may comprise, but are not limited to, tasksrelated to analysis of data received via the receiver 284, and tasksrelated to generating data to be transmitted via the transmitter 286.These tasks may further comprise medium access control (MAC) layerfunctions as specified by pertinent standards.

The receiver 284 may be adapted to perform digital receiver functionsthat may comprise, but are not limited to, fast Fourier transformprocessing, beamforming processing, equalization, demapping,demodulation control, deinterleaving, depuncture, and decoding. Thetransmitter 286 may perform digital transmitter functions that comprise,but are not limited to, coding, puncture, interleaving, mapping,modulation control, inverse fast Fourier transform processing,beamforming processing. The RF front end 280 may receive analog RFsignals via antennas 276 a, . . . , 276 n, converting the RF signal tobaseband and generating a digital equivalent of the received analogbaseband signal. The digital representation may be a complex quantitycomprising I and Q components. The RF front end 280 may also transmitanalog RF signals via an antenna 278 a, . . . , 278 n, converting adigital baseband signal to an analog RF signal.

In operation, the processor 282 may receive data from the receiver 284.The processor 282 may communicate received data to the basebandprocessor 272 for analysis and further processing. The basebandprocessor 272 may generate data to be transmitted via an RF channel bythe transmitter 286. The baseband processor 272 may communicate the datato the processor 282. The processor 282 may generate a plurality of bitsthat are communicated to the receiver 284. The processor 282 maygenerate signals to control the operation of the modulation process inthe transmitter 286, and of the demodulation process in the receiver284.

FIG. 2 b is an exemplary block diagram of a transceiver comprisingtransmitter and a receiver with adaptive modulation/demodulation for aMIMO system, which may be utilized in accordance with an embodiment ofthe invention. With reference to FIG. 2 b is shown a transmitter 200, areceiver 201, a processor 240, a baseband processor 142, a plurality oftransmitter antennas 115 a . . . 115 n, and a plurality of receiverantennas 117 a . . . 117 n. The transmitter 200 may comprise a transmitmodulation control block 236, a coding block 102, a puncture block 104,an interleaver block 106, a plurality of mapper blocks 108 a . . . 108n, a plurality of inverse fast Fourier transform (IFFT) blocks 110 a . .. 110 n, a beamforming V matrix block 112, and a plurality of digital toanalog (D to A) conversion and antenna front end blocks 114 a . . . 114n. The receiver 201 may comprise a receive demodulation control block234, a plurality of antenna front end and analog to digital (A to D)conversion blocks 116 a . . . 116 n, a beamforming U* matrix block 118,a plurality of fast Fourier transform (FFT) blocks 120 a . . . 120 n, achannel estimates block 122, an equalizer block 124, a plurality ofdemapper blocks 126 a . . . 126 n, a deinterleaver block 128, adepuncture block 130, and a Viterbi decoder block 132. The transmitmodulation control block 236 may enable control over the selection ofmodulation techniques utilized in the transmitter 200. The receivedemodulation control block 234 may enable control over the selection ofdemodulation techniques utilized in the receiver 201. In operation, thetransmit modulation control block 236 may enable control of modulationtechniques applied by each of the plurality of mapper blocks 108 a . . .108 n individually, on a per-stream basis. The receive demodulationcontrol block 234 may enable control of demodulation techniques appliedby each of the plurality of demapper blocks 126 a . . . 126 nindividually, on a per-stream basis.

The processor 240 may perform digital receiver and/or transmitterfunctions in accordance with applicable communications standards. Thesefunctions may comprise, but are not limited to, tasks performed at lowerlayers in a relevant protocol reference model. These tasks may furthercomprise the physical layer convergence procedure (PLOP), physicalmedium dependent (PMD) functions, and associated layer managementfunctions.

In operation, per-stream control of the mapper blocks 108 a . . . 108 nmay control the number of bits assigned to one or more individualstreams, b_(st)(i), to ensure that the sum of bits across the pluralityof streams equals the aggregate number of bits in the codingrate-adapted data block, b_(db), as shown in equation[1]. The processor240 may receive decoded data from the Viterbi decoder 132. The processor240 may communicate received data to the baseband processor 142 foranalysis and further processing. The processor 240 may also communicatedata received via the RF channel, by the receiver 101, to the channelestimates block 122. This information may be utilized by the channelestimates block 122, in the receiver 101, to compute channel estimatesfor a received RF channel. The baseband processor 142 may generate datato be transmitted via an RF channel by the transmitter 100. The basebandprocessor 142 may communicate the data to the processor 240. Theprocessor 240 may generate a plurality of bits that are communicated tothe coding block 102. The processor 240 may generate signals to controlthe operation of the transmit modulation control block 236, and of thereceive demodulation control block 234.

The elements shown in FIG. 2 b may comprise components that may bepresent in an exemplary embodiment of a wireless communicationsterminal. One exemplary embodiment of a may be a wireless communicationstransmitter comprising a transmitter 200, a processor 240, and abaseband processor 142. Another exemplary embodiment of a may be awireless communications receiver comprising a receiver 201, a processor240, and a baseband processor 142. Another exemplary embodiment of a maybe a wireless communications transceiver comprising a transmitter 200, areceiver 201, a processor 240, and a baseband processor 142.

FIG. 3 is an exemplary block diagram of a transceiver comprising atransmitter and a receiver with adaptive modulation/demodulation andcoding/decoding for a MIMO system, which may be utilized in accordancewith an embodiment of the invention. With reference to FIG. 3 there isshown a transmitter 300, a receiver 301, a processor 350, a basebandprocessor 142, a plurality of transmitting antennas 115 a . . . 115 n,and a plurality of receiving antennas 117 a . . . 117 n. The transmitter300 may comprise a plurality of puncture blocks 304 a, . . . , 304 n, aplurality of interleaver blocks 306 a, . . . , 306 n, a transmit codingcontrol block 340, and a plurality of blocks as shown in the transmitter200 (FIG. 2 b), the coding block 102, the plurality of mapper blocks 108a, . . . , 108 n, and the plurality of IFFT blocks 110 a, . . . , 110 n.The transmitter 300 may further comprise the beamforming V matrix block112, and the plurality of digital to analog conversion and antenna frontend blocks 114 a, . . . , 114 n, and the transmit modulation controlblock 236. The receiver 301 may comprise a plurality of deinterleaverblocks 328 a, . . . , 328 n, a plurality of depuncture blocks 330 a, . .. , 330 n, a receive coding control block 338, and a plurality of blocksas shown in the receiver 201 (FIG. 2 b), the plurality of antenna frontend and digital to analog conversion blocks 116 a, . . . , 116 n, thebeamforming U* matrix block 118, and the plurality of FFT blocks 120 a,. . . , 120 n. The receiver 301 may further comprise the channelestimates block 122, the equalizer block 124, the plurality of demapperblocks 126 a, . . . , 126 n, and the Viterbi decoder block 132, and thereceive demodulation control block 234.

In the transmitter 300, puncture and interleaving may be performedindividually on a per-stream basis. The output from the plurality ofpuncture blocks 304 a, . . . , 304 n may be communicated to theplurality of interleaver blocks 306 a, . . . , 306 n. Each punctureblock in the plurality 304 a, . . . , 304 n may communicate its outputto a corresponding one of the plurality of interleaver blocks 306 a, . .. , 306 n. The output from the plurality of interleaver blocks 306 a, .. . , 306 n may be communicated to the plurality of mapper blocks 108 a,. . . , 108 n. Each of the plurality of interleaver blocks 306 a, . . ., 306 n may communicate its output to a corresponding one of theplurality of mapper blocks 108 a, . . . , 108 n. The transmit codingcontrol block 340 may enable control over the application of punctureutilized in the transmitter 300.

In the receiver 301, depuncture and deinterleaving may be performedindividually on a per-stream basis. Each deinterleaver block 328 a, . .. , 328 n may receive input from a plurality of demapper blocks 126 a, .. . , 126 n with each of the plurality of deinterleaver blocks 328 a, .. . , 328 n receiving input from a corresponding one of the plurality ofdemapper blocks 126 a, . . . , 126 n. Each depuncture block 330 a, . . ., 330 n may receive input from a plurality of deinterleaver blocks 328a, . . . , 328 n with each of the plurality of depuncture blocks 330 a,. . . , 330 n receiving input from a corresponding one of the pluralityof deinterleaver blocks 328 a, . . . , 328 n. The output from each ofthe plurality of depuncture blocks 330 a, . . . , 330 n may becommunicated to the Viterbi decoder block 132. The receive decodingcontrol block 338 may enable control over the application of depunctureutilized in the receiver 301.

The processor 350 may perform digital receiver and/or transmitterfunctions in accordance with applicable communications standards. Thesefunctions may comprise, but are not limited to, tasks performed at lowerlayers in a relevant protocol reference model. These tasks may furthercomprise the physical layer convergence procedure (PLOP), physicalmedium dependent (PMD) functions, and associated layer managementfunctions.

In operation, the transmit coding control block 340 may enable controlof puncture applied by each of the plurality of puncture blocks 304 a, .. . , 304 n individually, on a per-stream basis. The per-stream controlof puncture may enable the coding rate to vary on a per-stream basis.The receive coding control block 338 may enable control of depunctureapplied by each of the plurality of depuncture blocks 330 a, . . . , 330n individually, on a per-stream basis. The per-stream control ofdepuncture may enable the receiver 301 to adapt to differences in thecoding rate of the received signal on a per-stream basis.

The processor 300 may receive decoded data from the Viterbi decoder 132.The processor 240 may communicate received data to the basebandprocessor 142 for analysis and further processing. The processor 350 mayalso communicate data received via the RF channel, by the receiver 101,to the channel estimates block 122. This information may be utilized bythe channel estimates block 122, in the receiver 101, to compute channelestimates for a received RF channel. The baseband processor 142 maygenerate data to be transmitted via an RF channel by the transmitter100. The baseband processor 142 may communicate the data to theprocessor 3500. The processor 350 may generate a plurality of bits thatare communicated to the coding block 102. The processor 350 may generatesignals to control the operation of the transmit modulation controlblock 236, and of the receive demodulation control block 234. Theprocessor 350 may generate signals to control the operation of thetransmit coding control block 340, and of the receive decoding controlblock 338.

The elements shown in FIG. 3 may comprise components that may be presentin an exemplary embodiment of a wireless communications terminal. Oneexemplary embodiment of a may be a wireless communications transmittercomprising a transmitter 300, a processor 340, and a baseband processor142. Another exemplary embodiment of a may be a wireless communicationsreceiver comprising a receiver 301, a processor 340, and a basebandprocessor 142. Another exemplary embodiment of a may be a wirelesscommunications transceiver comprising a transmitter 300, a receiver 301,a processor 340, and a baseband processor 142.

In one aspect of the invention, a system for communicating informationin a MIMO communications system may comprise a receiver that may beadapted to select, for a plurality of spatial streams, a modulation typeand/or coding rate. The receiver may communicate at least one message,via an RF channel, that comprises a plurality of modulation types and/orcoding rates. The receiver may be configured to receive subsequent databased on at least one selected modulation type and/or coding rate. Inanother aspect of the invention, the system may comprise a transmitterthat may receive a message, via an RF channel, that comprises aspecification of a plurality of modulation types and/or coding rates,for a plurality of spatial streams. The system may be configured totransmit subsequent data based on at least one of the receivedmodulation types and/or coding rates.

Channel sounding may comprise a plurality of methods by which atransmitter, for example, transmitter 200, and a receiver, for example,receiver 201, may exchange information in a closed loop system. Theexchanged information may be utilized by a transmitter such that thetransmitter may be configured to transmit subsequent data based on amodulation type and/or coding rate. The exchanged information may beutilized to configure the receiver to receive subsequent data based on amodulation type and/or coding rate. Channel sounding may enable thetransmitter to transmit, and the receiver to receive, based on a commonmodulation type and/or coding rate.

A frame structure for channel sounding which may utilize a MIMO moderequest frame, a MIMO channel request frame, a MIMO mode response frame,and a MIMO channel response frame are described in U.S. application Ser.No. 11/052,353 filed Feb. 7, 2005, which is hereby incorporated hereinby reference in its entirety.

In a MIMO system, various embodiments of the invention may enable atransmitter, for example, transmitter 200, and a receiver, for example,receiver 201, to utilize channel sounding mechanisms to exchangeinformation that specifies a modulation type and/or coding rate for eachof a plurality of spatial streams. The exchanged information may beutilized to configure the transmitter to transmit subsequent data via anindividual spatial stream among a transmitted plurality of spatialstreams based on a modulation type and/or coding rate. The exchangedinformation may be utilized to configure the receiver to receivesubsequent data via a corresponding individual spatial stream among areceived plurality of spatial streams based on a modulation type and/orcoding rate. Channel sounding may enable the transmitter to transmit viaan individual spatial stream, and the receiver to receive via acorresponding individual spatial stream, based on a common modulationtype and/or coding rate.

In an open loop MIMO system, a transmitter 100, 200, or 300, and areceiver 101, 201, or 301, may not utilize channel sounding closed loopfeedback methods. Instead, the transmitter may utilize a “back off”method to select a modulation type and/or coding rate for a plurality ofspatial streams. In an open loop system, the transmitter may select amodulation type and/or coding rate to be utilized in transmitting datato the receiver. If the receiver successfully receives the transmitteddata, an acknowledgement may be transmitted. Upon receipt of theacknowledgement, the transmitter may modify a previously selectedmodulation type and/or coding rate to increase the data rate ofsubsequent transmitted data. If the receiver does not successfullyreceive the transmitted data, an acknowledgement may not be transmitted.If the transmitter does not receive an acknowledgement, the transmittermay modify a previously selected modulation type and/or coding rate todecrease the data rate of subsequent transmitted data.

FIG. 4 shows an exemplary graph of throughput versus SNR simulations fora 2×2 system utilizing a 40 MHz D-type channel with perfect channelestimation based on MMSE-LE for packet size of 1000 bytes, in accordancewith an embodiment of the invention. With reference to FIG. 4 there isshown results from a simulation of an open loop system 402, results froma simulation of an adaptive modulation system 404, results from asimulation of an adaptive modulation and coding system 406, and resultsfrom a simulation of a TGn Sync (nSync) proposal 408. As illustrated inFIG. 4, for a given throughput, the SNR performance required in anadaptive modulation system 404 may be within 2 dB of the SNR performanceof an adaptive modulation and coding system 406. Either the adaptivemodulation system 404, or the adaptive modulation and coding system 406,may achieve a given level of throughput at a lower SNR than in the nSyncproposal 408. In this regard, the adaptive modulation system 404 mayrepresent a suitable alternative to a system that utilizes adaptivemodulation and coding 406.

FIG. 5 illustrates an exemplary training sequence for adaptivemodulations, which may be utilized in connection with an embodiment ofthe invention. With reference to FIG. 5, there is shown a first antenna500, and a second antenna 501. The physical layer protocol data unit(PPDU) transmitted by the first antenna 500 may comprise a shortsequence field 502, a training symbol guard interval (GI2) field 504, along sequence field 506, a guard interval (GI) field 508, a SIG-N field510, a plurality of guard interval fields 512 a . . . 512 b, and aplurality of data fields 514 a . . . 514 b. The message transmitted bythe second antenna 501 may comprise a short sequence field 522, atraining symbol guard interval field 524, a long sequence field 526, aguard interval field 528, a SIG-N field 530, a plurality of guardinterval fields 532 a, . . . , 532 b, and a plurality of data fields 534a, . . . , 534 b. A physical layer service data unit (PSDU) may comprisea header and a data payload. The preamble of the PSDU transmitted by thefirst antenna 500 may comprise a short sequence field 502, and a longsequence field 506. The header portion of the PSDU transmitted by thefirst antenna 500 may comprise the SIG-N field 510. The data payload ofthe PSDU transmitted by the first antenna 500 may comprise plurality ofdata fields 514 a, . . . , 514 b. The preamble to the PSDU transmittedby the second antenna 501 may comprise a short sequence field 522, and along sequence field 526. The header portion of the PSDU transmitted bythe second antenna 501 may comprise the SIG-N field 530. The datapayload of the PSDU transmitted by the second antenna 501 may compriseplurality of data fields 534 a, . . . , 534 b.

The short sequence field 502 may comprise a plurality of short trainingsequence symbols, for example, 10 short training sequence symbols. Eachshort training sequence symbol may comprise transmission of informationfor a defined time interval, for example, 800 nanoseconds (ns). Theduration of the short sequence field 502 may comprise a time interval,for example, 8 microseconds (μs). The short sequence field 502 may beutilized by a receiver, for example, receiver 201, for a plurality ofreasons, for example, signal detection, automatic gain control (AGC) forlow noise amplification circuitry, diversity selection such as performedby rake receiver circuitry, coarse frequency offset estimation, andtiming synchronization.

The training symbol guard interval field 504 may comprise a timeinterval during which the first antenna 500 does not transmitinformation via an RF channel. The duration of the training symbol guardinterval field 504 may comprise a time interval, for example, 1.6 μs.The training symbol guard interval field 504 may be utilized by areceiver, for example, receiver 201, to reduce the likelihood ofinter-symbol interference between a preceding symbol, for example, asymbol transmitted during a short sequence field 502, and a succeedingsymbol, for example, a symbol transmitted during a long sequence field506.

The long sequence field 506 may comprise a plurality of long trainingsymbols, for example, 2 long training symbols. Each long training symbolmay comprise transmission of information for a defined time interval,for example, 3.2 μs. The duration of the long training sequence,including the duration of the long sequence field 506, and the precedingtraining symbol guard interval field 504, may comprise a time intervalof, for example, 8 μs. The long training sequence field 506 may beutilized by a receiver, for example, receiver 201, for a plurality ofreasons, for example, fine frequency offset estimation, and channelestimation.

The guard interval field 508 may comprise a time interval during whichthe first antenna 500 does not transmit information via an RF channel.The duration of guard interval field 508 may comprise a time interval,for example, 800 ns. The guard interval field 508 may be utilized by areceiver, for example, receiver 201, to reduce the likelihood ofinter-symbol interference between a preceding symbol, for example, asymbol transmitted during a long sequence field 506, and a succeedingsymbol, for example, a symbol transmitted during the signal SIG-N field510.

The signal SIG-N field 510 may comprise, for example, a signal symbol.Each signal symbol may comprise transmission of information for adefined time interval, for example, 3.2 μs. The duration of the singlesymbol, including the duration of the signal SIG-N field 510, and thepreceding guard interval field 508, may comprise a time interval, forexample, 4 μs. The signal SIG-N field 510 may be utilized by a receiver,for example, receiver 201, to establish a plurality of configurationparameters associated with receipt of a physical layer service data unit(PSDU) via an RF channel.

The guard interval field 512 a may comprise a time interval during whichthe first antenna 500 does not transmit information via an RF channel.The duration of guard interval field 512 a may comprise a time interval,for example, 800 ns. The guard interval field 512 a may be utilized by areceiver, for example, receiver 201, to reduce the likelihood ofinter-symbol interference between a preceding symbol, for example, asymbol transmitted during a signal SIG-N field 510, and a succeedingsymbol, for example, a symbol transmitted during a the data field 514 a.Each successive guard interval field in the plurality of guard intervalfields 512 a, . . . , 512 b may be utilized by a receiver, for example,receiver 201, to reduce the likelihood of inter-symbol interferencebetween a preceding symbol, for example, a symbol transmitted during theplurality of data fields 514 a, . . . , 514 b, and a succeeding symbolin the plurality of data fields 514 a, . . . , 514 b.

A data field in the plurality of data fields 514 a, . . . , 514 b maycomprise, for example, a data symbol. Each data symbol may comprisetransmission, by the first antenna 500, of information for a definedtime interval, for example, 3.2 μs. The duration of each data interval,including the duration of a data field in the plurality of data fields514 a, . . . , 514 b, and the preceding guard interval field in theplurality of guard interval fields 512 a, . . . , 512 b, may comprise atime interval, for example, 4 μs. The plurality of data fields 514 a, .. . , 514 b may be utilized by a receiver, for example, receiver 201,receive information that is contained in a PSDU data payload receivedvia an RF channel.

The short sequence field 522, training symbol guard interval field 524,long sequence field 526, guard interval 528, and signal SIG-N field 530may comprise time shifted, or cyclically shifted, representations of thecorresponding short sequence field 502, training symbol guard intervalfield 504, long sequence field 506, guard interval 508, and signal SIG-Nfield 510. The start of transmission of the cyclically shifted versionshort sequence field 522 by the second antenna 501 may precede the startof transmission of the short sequence field 502 by the first antenna 500by an interval, for example, 400 ns. The start of transmission of thecyclically shifted version long sequence field 526 by the second antenna501 may precede the start of transmission of the long sequence field 506by the first antenna 500 by an interval, for example, 1600 ns. The startof transmission of the cyclically shifted version signal SIG-N field 530by the second antenna 501 may precede the start of transmission of thesignal SIG-N field 510 by the first antenna 500 by an interval, forexample, 1600 ns.

The guard interval field 532 a may comprise a time interval during whichthe second antenna 501 does not transmit information via an RF channel.The duration of guard interval field 532 a may comprise a time interval,for example, 800 ns. The guard interval field 532 a may be utilized by areceiver, for example, receiver 201, to reduce the likelihood ofinter-symbol interference between a preceding symbol, for example, asymbol transmitted during a signal SIG-N field 530, and a succeedingsymbol, for example, a symbol transmitted during a the data field 534 a.Each successive guard interval field in the plurality of guard intervalfields 532 a, . . . , 532 b may be utilized by a receiver, for example,receiver 201, to reduce the likelihood of inter-symbol interferencebetween a preceding symbol, for example, a symbol transmitted during theplurality of data fields 534 a, . . . , 534 b, and a succeeding symbolin the plurality of data fields 534 a, . . . , 534 b.

The data field in the plurality of data fields 534 a . . . 534 b maycomprise, for example, a data symbol. Each data symbol may comprisetransmission, by the second antenna 501, of information for a definedtime interval, for example, 3.2 μs. The duration of each data interval,including the duration of a data field in the plurality of data fields534 a, . . . , 534 b, and the preceding guard interval field in theplurality of guard interval fields 532 a, . . . , 532 b, may comprise atime interval, for example, 4 μs. The plurality of data fields 534 a, .. . , 534 b may be utilized by a receiver, for example, receiver 201,receive information that is contained in a PSDU data payload receivedvia an RF channel. The short sequence field 502, and the long sequencefield 506, are specified in IEEE resolution 802.11.

In operation, short sequence and long sequence fields may be transmittedby the first antenna 500, of a transmitter, for example, transmitter200, and received by a receiver, for example, receiver 201. For example,the receiver may compare a received long sequence field against the wellknown expected values to determine an extent to which transmissionimpairments may exist in the downlink channel. Channel estimates may bederived for the downlink channel. The channel estimates may comprise SNRinformation and may comprise information about individual spatialstreams that may be transmitted via the downlink channel.

The short sequence field 522, and the long sequence field 526, arespecified in IEEE resolution 802.11. The short sequence and longsequence fields may be transmitted by the second antenna 501, of atransmitter, for example, transmitter 200, and received by a receiver,for example, receiver 201. For example, the receiver may compare areceived long sequence field against known expected values to determinean extent to which transmission impairments may exist in the downlinkchannel, and therefore, to derive channel estimates for the downlinkchannel. The channel estimates may comprise SNR information and maycomprise information about individual spatial streams that may betransmitted via the RF or downlink channel.

The preamble portion and header portion of the PSDU transmitted by thefirst antenna 500 may be transmitted utilizing a known modulation typeand coding rate. The utilization of a known modulation type and codingrate may enable a transmitter, for example, transmitter 200, and areceiver, for example, receiver 201, to communicate until modulationtype and coding rate information has been exchanged. The modulation typemay comprise binary phase shift keying (BPSK), for example. The codingrate may be represented as ½. The modulation type and coding rate mayrepresent the lowest data rate at which data may be transmitted via aspatial stream in an RF channel. The header transmitted by the firstantenna comprising the signal SIG-N field 510, and the plurality of datafields 514 a . . . 514 b, may comprise a physical layer protocol dataunit (PPDU).

Beamforming, which may also be referred to as Eigenbeamforming, may beutilized at the beginning of the long training sequence (LTS), which maycorrespond to the beginning of the training symbol guard interval 504.Alternatively, beamforming may be utilized at the start of reception ofthe data payload, which may correspond to the beginning of the guardinterval 512 a. The receiver may determine that a received frame isprocessed utilizing adaptive modulation based on the signal SIG-N field510. Adaptive modulation may comprise modifying at least one modulationand/or coding rate for at least one transmitted spatial stream based onchannel feedback information in a closed loop MIMO system.

The preamble portion and header portion of the PSDU transmitted by thesecond antenna 501 may be transmitted utilizing a particular modulationtype and coding rate. The utilization of a particular modulation typeand coding rate may enable a transmitter, for example, transmitter 200,and a receiver, for example, receiver 201, to communicate untilmodulation type and coding rate information has been exchanged. Themodulation type may comprise binary phase shift keying (BPSK). Thecoding rate may be represented as ½. The modulation type and coding ratemay represent the lowest data rate at which data may be transmitted viaa spatial stream in an RF channel. The header transmitted by the firstantenna comprising the signal SIG-N field 530, and the plurality of datafields 534 a . . . 534 b, may comprise a PPDU.

Eigenbeamforming may be utilized at the beginning of the long trainingsequence (LTS), which may correspond to the beginning of the trainingsymbol guard interval 524. Alternatively, beamforming may be utilized atthe start of reception of the data payload, which may correspond to thebeginning of the guard interval 532 a. The receiver may determine that areceived frame is processed utilizing adaptive modulation based on thesignal SIG-N field 530. Adaptive modulation may comprise modifying atleast one modulation and/or coding rate for at least one transmittedspatial stream based on channel feedback information in a closed loopMIMO system.

FIG. 6 illustrates an exemplary SIG-N field, in accordance with anembodiment of the invention. With reference to FIG. 6 there is shown anumber of spatial streams (NSS) field 602, a number of transmittingantenna (NTX) field 604, a bandwidth (BW) field 606, a coding rate (R)field 608, an error correcting code type (CT) field 610, and aconstellation types (CONs) field 612. Also illustrated in FIG. 6 is alength (LEN) field 614, a last PSDU indicator (LPI) field 616, a closedloop (Clsd) field 618, a RSVD field 620, a cyclical redundancy check(CRC) field 622, and a tail field 624.

The number of spatial streams field 602 may comprise 3 bits of binarydata. The number of spatial streams field 602 may indicate the number ofspatial streams utilized in transmitting information between atransmitter, for example, 200, and a receiver, for example, 201. In aMIMO system the number of spatial streams may represent a number, forexample, 1, 2, 3, or 4. The number of transmitting antenna field 604 maycomprise, for example, 3 bits of binary data. The number of transmittingantenna field 604 may indicate the number of transmitting antenna, forexample, antenna 500, utilized in transmitting information between atransmitter and a receiver. In a MIMO system the number of transmittingantenna may represent a number, for example, 1, 2, 3, or 4. Thebandwidth field 606 may comprise 2 bits of binary data. The bandwidthfield 606 may indicate the bandwidth that is utilized for transmittinginformation between a transmitter and a receiver. In a MIMO system thebandwidth may represent a bandwidth, for example, 20 MHz, or 40 MHz,where 20 MHz may correspond to utilization of a 20 MHz RF channel, and40 MHz may correspond to utilization of a 40 MHz RF channel. The codingrate field 608 may comprise 3 bits of binary data. The coding rate field608 may indicate the coding rate that is utilized in transmitting aphysical layer service data unit (PSDU) via an antenna. In a MIMOsystem, the coding rate may represent a number, for example, ½, ⅔, ¾, or⅚. The error correcting code type field 610 may comprise 2 bits ofbinary data. The error correcting code type field 610 may indicate theerror correcting code type that is utilized in transmitting informationvia an antenna. In a MIMO system, the error correcting code type mayrepresent an error correcting coding method, for example, binaryconvolutional coding (BCC), or low density parity coding (LDPC). Theconstellation types field 612 may comprise 7 bits of binary data. Theconstellation types field 612 may indicate the constellation type, ormodulation type, which is utilized in transmitting a PSDU in one or morespatial streams via an antenna. In a MIMO system, the modulation typemay represent a constellation indicating the number of binary bits thatmay be encoded in a symbol, for example, binary phase shift keying(BPSK), quaternary phase shift keying (QPSK), 16 level quadratureamplitude modulation (16 QAM), 64 level QAM (64 QAM), or 256 level QAM(256 QAM).

The length field 614 may comprise information that indicates the numberof binary octets of data payload information, for example, in datafields 514 a, . . . , 514 b transmitted via an antenna, for exampleantenna 500. The indicator LPI field 616 may comprise 1 bit of binaryinformation. The indicator LPI field 616 may comprise information thatindicates whether the data payload, for example, the plurality of datafields 514 a . . . 514 b, represent that last information comprised in amessage. The closed loop field 618 may indicate whether a transmitter,for example, transmitter 200, utilized MIMO closed loop feedbackinformation in transmitting information via an antenna. The reservedfield 620 may comprise 9 bits of binary information. The reserved field620 may have no assigned usage. The configuration field 504 may comprise16 bits of binary information. The cyclical redundancy check field 622may comprise 4 bits of binary information. The cyclical redundancy checkfield 622 may comprise information that may be utilized by a receiver,for example, receiver 201, to detect the presence of errors in areceived PPDU, for example, the header SIG-N field 510, and data, forexample, the plurality of data fields 514 a . . . 514 b. The tail field624 may comprise 6 bits of binary information. The tail field 624 maycomprise information that is appended after the cyclical redundancycheck field 622 to pad the SIG-N field to a desired length.

In operation, in a closed loop MIMO system, the constellation typesfield 612, may be utilized by a receiver, for example, receiver 201, toselect, for a plurality of spatial streams, at least one modulationtype. A receiver may select a unique modulation type and/or coding ratefor each of a plurality of spatial streams transmitted by an antenna,for example, antenna 500. The selected modulation types and coding ratesmay be communicated via an uplink channel. A transmitter, for exampletransmitter 200, may receive the selected modulation types and codingrates transmitted via an RF channel that comprises specification of aplurality of modulation types and/or coding rates for a plurality ofspatial streams. The transmitter may be configured for transmittingsubsequent data based on at least one received modulation type and/orcoding rate.

The modulation and/or coding rate may comprise a specification of one ofthe plurality of spatial streams by the receiver, and a specification ofa corresponding spatial stream transmitted as a part of at least aportion of a plurality of spatial streams by a transmitter. Atransmitter may receive a specification of a plurality of modulationtypes and/or coding rates for a plurality of spatial streams. Thetransmitter may then utilize each of the plurality of modulation typesand/or coding rates specified by a receiver, for a plurality of spatialstreams, to transmit subsequent data utilizing a corresponding one of aplurality of transmitted spatial streams. A transmitter may receive aspecification of a plurality of modulation types and/or coding rates fora plurality of spatial streams. The transmitter may then utilize atleast one specified modulation type and/or coding rate to transmitsubsequent data utilizing at least one spatial stream.

In one embodiment of the invention, in a closed loop MIMO system, areceiver, for example, receiver 201, may generate channel feedbackinformation based on at least one SNR for a plurality of spatialstreams. The generated channel feedback information may be communicatedvia an uplink channel. A transmitter, for example, transmitter 200, mayreceive the channel feedback information based on at least one SNRobserved by the receiver for a plurality of spatial streams. Thetransmitter may select a plurality of modulation types and/or codingrates for a plurality of spatial streams. The transmitter may beconfigured for transmitting subsequent data based on at least oneselected modulation type and/or coding rate that had been selected basedon the channel feedback information.

In another embodiment of the invention, in an open loop MIMO system, atransmitter, for example transmitter 200, may select a plurality ofmodulation types and/or coding rates for a plurality of spatial streams.The transmitter may configure for transmitting subsequent data based onat least one selected modulation type and/or coding rate.

In either closed loop, or open loop, MIMO systems, the transmitter, forexample, transmitter 200, may communicate to the receiver, for example,receiver 201, information comprising specification of the modulationtypes and/or coding rate types that were utilized in transmittingsubsequent data via the signal SIG-N message field, for example, theexemplary SIG-N field shown in FIG. 6, contained in a PPDU. Theconstellation types field 612 may comprise specification of themodulation types utilized in a plurality of spatial streams that weretransmitted via a transmitting antenna, for example, antenna 500.Whether subsequent data was transmitted utilizing a closed loop method,or an open loop method may be determined by a receiver based on theclosed loop field 604.

If the closed loop field 618 Clsd=0 and the number of spatial streams(NSS), represented by the number of spatial streams field 602, isapproximately equal to, or one less than, the number of transmittingantenna (NTX) represented by the number of transmitting antenna field604, this may indicate that a transmitter, for example, the transmitter200, may be transmitting data without utilizing beamforming, and insteadutilizing spatial division multiplexing (SDM), or space-time blockcoding (STBC). If the closed loop field 618 Clsd=1 and the constellationtypes field 612 indicates that each of the NSS number of spatial streamsutilizes the same modulation type, this may indicate that thetransmitter may be transmitting utilizing Eigenbeamforming, and notutilizing streamloading, or utilizing individual per-stream adaptivemodulation. If streamloading is not utilized, each spatial steam mayutilize an equivalent modulation type, and the data rate for eachspatial stream may be equivalent. If streamloading is utilized, somespatial streams may utilize different modulation types, and the datarates for some spatial streams may differ from those of other spatialstreams. Adaptive modulation may enable a transmitter to adapt the datarate for a spatial stream, to increase or decrease, based on channelfeedback information. In various embodiments of the invention, themodulation type, and/or coding rate, may be adapted individually foreach spatial stream.

An OFDM symbol comprising a plurality of tones may be transmitted via anRF channel, where each tone may be transmitted at a frequency selectedfrom a range of subcarrier frequencies. The SNR for a given spatialstream transmitted via an RF channel may vary by frequency such that atone sent at frequency f₁ may have an SNR_(f1) that is different fromthe SNR for a tone sent at a different frequency f₂, SNR_(f2). Anaggregate SNR may be determined for a spatial mode by computing ageometric mean SNR based upon the individual SNR_(fi); from among thefrequencies f_(i) that may be transmitted via an RF channel. Theaggregate geometric SNR, which may be referred to as SNR_(geo), may beexpressed as in the following equation:

$\begin{matrix}{{{SNR}_{geo} = \sqrt[k]{\prod\limits_{f_{i} = 1}^{k}\;{SNR}_{f_{i}}}},} & {{equation}\mspace{14mu}\lbrack 2\rbrack}\end{matrix}$wherek may be equal to the number of tones comprised in an OFDM symbol thatmay be transmitted via an RF channel, π may represent the multiplicativeproduct of the SNRs for individual tones, and the expression in equation[2] may refer to the aggregate geometric SNR being equal to the k^(th)root of the product individual SNRs from each of the k tones.

In accordance with an embodiment of the invention, a geometric SNR maybe determined for each spatial mode SNR_(geo,i). Upon determining eachof the SNR_(geo,i), an algorithm, for example, Aslanis formula may beutilized to determine a number of binary bits that may be transmittedamong each of the spatial modes. For the i^(th) spatial mode, the numberof bits that may be transmitted at approximately the same time, b_(i),may be calculated by Aslanis formula as in the following equation:b _(i)=log₂(1+SNR_(geo,i)), where  equation[3]the expression in equation[3] computes a base 2 logarithm for thegeometric SNR for spatial mode i.

A characteristic of the singular matrix that may be generated inassociation with Eigenbeamforming of a plurality of spatial modes:SNR_(geo,1)≧SNR_(geo,2)≧SNR_(geo,3)≧SNR_(geo,4)  equation[4]

Equation[4] may suggest that the SNR for a subsequent spatial streamamong a plurality of NSS spatial streams, may be less than or equal tothe SNR for a preceding spatial stream. This may, based on equation[3],further suggest that the number of binary bits, b_(i), that may beassigned to a spatial stream, i, may observe the following correspondingrelationship to equation[4]:b ₁ ≧b ₂ ≧b ₃ ≧b ₄  equation[5]

A modulation type may comprise a plurality of constellation points. Thenumber of constellation points may determine the number of binary bitsthat may be encoded in a symbol generated by the correspondingmodulation type. For a given modulation type, the minimum number ofconstellation points, CP_(i), required to encode a spatial modecomprising a plurality b_(i) number of binary bits may be representedas:CP_(i)≧2^(b) ^(i)   equation[6]

As a result of equations [4], [5], and [6], selection of a modulationtype, M_(i), from a plurality of modulation types M_(X), for a spatialstream, i, may enable selection of a modulation type, M_(j), for asubsequent spatial stream, j, such that the number of constellationpoints for M_(j) may be less than or equal to the number ofconstellation points for M_(i). Thus, M_(j) may be selected from aplurality of modulation types My where the number M_(Y) may be less thanor equal to the number M_(X).

Equations [7] and [8] may show vectors comprising exemplary values thatmay be utilized to show possible combinations of modulation types amonga plurality of spatial streams for NSS=4. In each equation, a modulationtype may be indicated based on the number of binary bits of informationthat may be modulated in a single symbol. For example, in BPSKmodulation a single bit of binary information may be contained in asingle symbol. For example, in QPSK modulation, 2 bits of binaryinformation may be contained in a single symbol. If no binaryinformation is transmitted via a spatial stream a 0 may be indicated. Inequations [7] and [8], each column may represent a unique combination ofmodulation types across spatial stream, while each row may represent anindividual spatial stream. The first row may represent modulation typesused in each combination for the first spatial stream. The second rowmay represent modulation types used in each combination for the secondspatial stream. The third row may represent modulation types used ineach combination for the third spatial stream. The fourth row mayrepresent modulation types used in each combination for the fourthspatial stream.

$\begin{matrix}\begin{bmatrix}1 & 1 & 1 & 1 \\0 & 1 & 1 & 1 \\0 & 0 & 1 & 1 \\0 & 0 & 0 & 1\end{bmatrix} & {{equation}\mspace{14mu}\lbrack 7\rbrack} \\\begin{bmatrix}2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 \\0 & 1 & 1 & 1 & 2 & 2 & 2 & 2 & 2 & 2 \\0 & 0 & 1 & 1 & 0 & 1 & 1 & 2 & 2 & 2 \\0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 & 1 & 2\end{bmatrix} & {{equation}\mspace{14mu}\lbrack 8\rbrack}\end{matrix}$

As indicated in equation[7], there may be 4 combinations of coding rateswhen the first stream utilizes BPSK. In the first combination, BPSKmodulation may be utilized in a first spatial stream with no informationtransmitted in spatial streams 2, 3, or 4. In the second combination,BPSK modulation may be utilized in the first and second spatial streams,with no information transmitted in spatial streams 3, or 4. As indicatedin equation[8], there may be 10 combinations of coding rates when thefirst stream utilizes QPSK. In the seventh combination from equation[8]QPSK modulation may be utilized in spatial streams 1 and 2, while BPSKmodulation may be utilized in spatial streams 3 and 4.

When the first spatial stream utilizes 16 QAM, equation[9] may showvectors comprising exemplary values that may be utilized to showpossible combinations of modulation types among a plurality of spatialstreams for NSS=4.

$\mspace{574mu}{{{equation}\mspace{14mu}\lbrack 9\rbrack}\begin{bmatrix}4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 \\0 & 1 & 1 & 1 & 2 & 2 & 2 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 \\0 & 0 & 1 & 1 & 0 & 1 & 1 & 2 & 2 & 2 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 \\0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4\end{bmatrix}}$

As indicated in equation[9], there may be 20 combinations of codingrates when the first stream utilizes 16 QAM. In this case, there may be10 combinations in which the second spatial stream utilizes 16 QAM, andanother 9 combinations in which the second spatial stream utilizes QPSKor BPSK. In one combination, no information may be transmitted inspatial streams 2, 3, or 4. In the seventh combination from equation[9],16 QAM modulation may be utilized in spatial stream 1, QPSK modulationmay be utilized in spatial stream 2, while BPSK modulation may beutilized in spatial streams 3 and 4.

When the first spatial stream utilizes 64 QAM, equation[10] may showvectors comprising exemplary values that may be utilized to showpossible combinations of modulation types among a plurality of spatialstreams for NSS=4.

$\mspace{565mu}{{{equation}\mspace{14mu}\lbrack 10\rbrack}\begin{bmatrix}6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 \\0 & 1 & 1 & 1 & 2 & 2 & 2 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 \\0 & 0 & 1 & 1 & 0 & 1 & 1 & 2 & 2 & 2 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 6 & 6 & 6 & 6 & 6 \\0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4 & 0 & 1 & 2 & 4 & 6\end{bmatrix}}$

As indicated in equation[10], there may be 35 combinations of codingrates when the first stream utilizes 64 QAM. In this case, there may be15 combinations in which the second spatial stream utilizes 64 QAM, andanother 19 combinations in which the second spatial stream utilizes 16QAM, QPSK or BPSK. In one combination, no information may be transmittedin spatial streams 2, 3, or 4. In the fifteenth combination fromequation[10], 64 QAM modulation may be utilized in spatial stream 1, 16QAM modulation may be utilized in spatial stream 2, QPSK modulation maybe utilized in spatial stream 3, while BPSK modulation may be utilizedin spatial stream 4.

When the first spatial stream utilizes 256 QAM, equation[11] may showvectors comprising exemplary values that may be utilized to showpossible combinations of modulation types among a plurality of spatialstreams for NSS=4.

$\begin{matrix}{\mspace{1285mu}{{{equation}\mspace{14mu}\lbrack 11\rbrack}\left\lbrack \begin{matrix}8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 \\0 & 1 & 1 & 1 & 2 & 2 & 2 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 & 6 \\0 & 0 & 1 & 1 & 0 & 1 & 1 & 2 & 2 & 2 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 6 & 6 & 6 \\0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4 & 0 & 1 & 2\end{matrix} \right.}} \\\left. \mspace{625mu}\begin{matrix}8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 \\6 & 6 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 & 8 \\6 & 6 & 0 & 1 & 1 & 2 & 2 & 2 & 4 & 4 & 4 & 4 & 6 & 6 & 6 & 6 & 6 & 8 & 8 & 8 & 8 & 8 & 8 \\4 & 6 & 0 & 0 & 1 & 0 & 1 & 2 & 0 & 1 & 2 & 4 & 0 & 1 & 2 & 4 & 6 & 0 & 1 & 2 & 4 & 6 & 8\end{matrix} \right\rbrack\end{matrix}$

As indicated in equation[11], there may be 56 combinations of codingrates when the first stream utilizes 256 QAM. In this case, there may be21 combinations in which the second spatial stream utilizes 256 QAM, andanother 34 combinations in which the second spatial stream utilizes 64QAM, 16 QAM, QPSK or BPSK. In one combination, no information may betransmitted in spatial streams 2, 3, or 4. In the thirty fifthcombination from equation[11], 256 QAM modulation may be utilized inspatial stream 1, while 64 QAM modulation may be utilized in spatialstreams 2, 3, and 4.

When the range of modulation types that may be utilized for a firstspatial stream comprises 256 QAM, 64 QAM, 16 QAM, QPSK, or BPSK theremay be a total of 125 combinations (4+10+20+35+56) of modulation typesamong the 4 spatial steams as indicated in equations [7], [8], [9],[10], and [11]. These 125 combinations may be uniquely identified in theconstellation types field 612 utilizing 7 bits of binary information.

In a MIMO system comprising 5 modulation types and 4 spatial streams,there may be a total of 625 potential combinations of modulation types.In this regard, 10 bits of binary information may be required touniquely identify each potential combination. Various embodiments of theinvention may utilize properties of Eigenvalue analysis of MIMO systemsto reduce the number of bits of binary information required to encode amodulation type among a plurality of modulation types to a spatialstream among a plurality of spatial streams. The reduction in the numberof required bits in various embodiments of the invention compared toother approaches may enable greater flexibility in the signal SIG-Nfield. The constellation types field 612 may further be extended byutilizing bits from the reserved field in the SIG-N field.

FIG. 7 is a flowchart illustrating exemplary steps for closed loopmodulation type requested by a receiver, in accordance with anembodiment of the invention. In the flowchart of FIG. 7, a receiver 201may determine a data rate by assigning a modulation type and/or codingrate per spatial stream. The modulation type and/or coding rateselections may be communicated to a transmitter 200 in a messagecomprising feedback information. With reference to FIG. 7, in step 702the approximate number of bits in a data block, b_(db), which may betransmitted simultaneously, may be determined. An index for anindividual spatial stream, i, may be initialized to a value equal to 1.In step 704 a receiver may compute geometric mean SNRs for each spatialstream. In step 706, the number of bits, b_(i), in the i^(th) spatialstream may be determined. In step 708 a receiver may select a modulationtype for the i^(th) spatial stream based on observed SNR and packeterror rate (PER) objectives. The selected modulation type may comprise asufficient number of constellation points to encode the number of bits,b_(i). In step 710 the data block variable, b_(db), may be decrementedby the number of bits, b_(i), to indicate the remaining number of bitsfrom the data block to be encoded. Step 712 may determine whether thecurrent value of the data block variable, b_(db), is greater than 0. Ifb_(db) is greater than 0, step 713 may establish that the number of bitsin a subsequent spatial stream will be less than or equal to the numberof bits in the current spatial stream. Step 714 may increment thespatial stream index i by 1 to refer to the subsequent spatial stream.Step 706 may follow step 714.

If b_(db) is not greater than 0, in step 716, a receiver may feed backthe selected modulation type for each spatial stream to a transmitter.Step 718 may determine if subsequent data was transmitted based onfeedback information. If not, in step 726 the transmitter may transmitsubsequent data to a receiver without utilizing beamforming. In step728, the transmitter may transmit subsequent data to the receiverindicating a selected modulation type for a spatial stream andindicating that the selected modulation type may not be based onfeedback information from the receiver.

If step 718 determines that subsequent data was transmitted based onfeedback information, step 720 may determine if adaptive modulations areenabled. If so, in step 722, the transmitter may transmit subsequentdata to the receiver based on prior feedback information from thereceiver, which indicates that beamforming was utilized along with theselected modulation types by spatial stream. If in step 720 it wasdetermined that beamforming was not utilized, in step 724, thetransmitter may transmit subsequent data to the receiver based onfeedback information from the receiver indicting that beamforming wasnot utilized and indicating a modulation type selected by the receiverfor a plurality of transmitted spatial streams.

FIG. 8 is a flowchart illustrating exemplary steps for closed loopmodulation type determined by a transmitter based on channel feedbackfrom a receiver, in accordance with an embodiment of the invention. Incomparison to the flowchart illustrated in FIG. 7, where a receiver 201may select a plurality of modulation types that are communicated asfeedback information to a transmitter 200, in the flowchart illustratedin FIG. 8, the receiver may communicate SNR information to thetransmitter. The transmitter may utilize the SNR information from thereceiver to select a plurality of modulation types for a correspondingplurality of spatial streams. The transmitter 200 may determine a datarate by assigning a modulation type and/or coding rate per spatialstream. The flowchart of FIG. 8 may differ from the flowchart of FIG. 7in steps 804, 808, and 816.

With reference to FIG. 8, in step 802 the approximate number of bits ina data block, b_(db), which may be transmitted simultaneously, may bedetermined. An index for an individual spatial stream, i, may beinitialized to a value equal to 1. In step 804, a transmitter mayreceive feedback information from the receiver that includes geometricmean SNR for each spatial stream. In step 806, the number of bits,b_(i), in the i^(th) spatial stream may be determined. In step 808 thetransmitter may select a modulation type for the i^(th) spatial streambased on observed SNR and packet error rate (PER) objectives. Theselected modulation type may comprise a sufficient number ofconstellation points to encode the number of bits, b_(i). In step 810,the data block variable, b_(db), may be decremented by the number ofbits, b_(i), to indicate the remaining number of bits from the datablock to be encoded. Step 812 may determine whether the current value ofthe data block variable, b_(db), is greater than 0. If b_(db) is greaterthan 0, step 813 may establish that the number of bits in a subsequentspatial stream will be less than or equal to the number of bits in thecurrent spatial stream. Step 814 may increment the spatial stream index,i, by 1 to refer to the subsequent spatial stream. Step 806 may followstep 814.

If b_(db) is not greater than 0, in step 816, the transmitter maytransmit subsequent data to the receiver based on the selectedmodulation type for each spatial stream. Step 818 may determine ifsubsequent data was transmitted based on feedback information. If not,in step 826, the transmitter may transmit subsequent data to a receiverwithout utilizing beamforming. In step 828, the transmitter may transmitsubsequent data to the receiver indicating a selected modulation typefor a spatial stream and indicating that the selected modulation typemay not be based on feedback information from the receiver.

If step 818 determines that subsequent data was transmitted based onfeedback information, step 820 may determine if adaptive modulations areenabled. If so, in step 822, the transmitter may transmit subsequentdata to the receiver based on prior feedback information from thereceiver, which indicates that beamforming was utilized along with theselected modulation types by spatial stream. If in step 820 it wasdetermined that beamforming was not utilized, in step 824, thetransmitter may transmit subsequent data to the receiver based onfeedback information from the receiver indicting that beamforming wasnot utilized and indicating a modulation type selected by the receiverfor a plurality of transmitted spatial streams.

FIG. 9 is a flowchart illustrating exemplary steps for open loopmodulation type determined by a transmitter, in accordance with anembodiment of the invention. In FIG. 9, the transmitter may selectmodulation types in an open loop MIMO system. With reference to FIG. 9,in step 902, the approximate number of bits in a data block, b_(db),which may be transmitted simultaneously, may be determined. An index foran individual spatial stream, i, may be initialized to a value equalto 1. In step 906, the number of bits, b_(i), in the i^(th) spatialstream may be determined. In step 908, the transmitter may select amodulation type for the i^(th) spatial stream. The selected modulationtype may comprise a sufficient number of constellation points to encodethe number of bits, b_(i). In step 910, the data block variable, b_(db),may be decremented by the number of bits, b_(i), to indicate theremaining number of bits from the data block to be encoded. Step 912 maydetermine whether the current value of the data block variable, b_(db),is greater than 0. If b_(db) is greater than 0, step 913 may establishthat the number of bits in a subsequent spatial stream will be less thanor equal to the number of bits in the current spatial stream. Step 914may increment the spatial stream index i by 1 to refer to a subsequentspatial stream. Step 906 may follow step 914.

If b_(db) is not greater than 0, in step 916 a transmitter may determinewhether to transmit data utilizing beamforming. The transmitter may makethis determination based on whether beamforming is currently beingutilized. The transmitter may also base the determination on the statusof successfully acknowledge frames at the receiver. If beamforming isutilized, in step 918, the transmitter may determine whether to assignmodulation types per spatial stream. If so, in step 922, the transmittermay transmit subsequent data to the receiver indicating beamforming, andindicating a selected modulation type per spatial stream. If beamformingis to be utilized but modulations are not to be assigned per spatialstream, in step 924 the transmitter may transmit subsequent data to thereceiver indicating beamforming and indicating a modulation type for aplurality of spatial streams. If beamforming is not utilized followingstep 916, in step 920 the transmitter may transmit subsequent data tothe receiver indicating a modulation type for a plurality of spatialstreams, and indicating that a modulation type is not based on feedbackfrom the receiver.

One embodiment of the invention may comprise a system for communicatinginformation in a communications system in which a transmitter 200 (FIG.2 b), in a MIMO communication system utilizing a plurality of modulationtypes and a plurality of spatial streams, may select a currentmodulation type for modulating a current spatial stream to betransmitted. The transmitter may select at least one subsequentmodulation type based on the selected current modulation type, formodulating at least one subsequent spatial stream to be transmitted. Thetransmitter may transmit a message indicating the selected currentmodulation type, and at least one selected subsequent modulation type,via an RF channel, to a receiver. The transmitter may also be configuredto transmit subsequent data based on the selected current modulationtype and/or at least one selected subsequent modulation type. Thetransmitter may encode a constellation field to uniquely identify acombination comprising the selected current modulation type, and atleast one subsequent selected modulation type. The number ofconstellation points comprised in a subsequent selected modulation typemay be less than or equal to the number of constellation pointscomprised in a selected current modulation type.

Another embodiment of the invention may comprise a system forcommunicating information in a communications system in which a receiver201 (FIG. 2 b), in a MIMO communication system, may select a currentmodulation type for modulating a current spatial stream to betransmitted. The receiver may select at least one subsequent modulationtype based on the selected current modulation type, for modulating atleast one subsequent spatial stream to be transmitted. The receiver maycommunicate a message indicating the selected current modulation typeand at least one selected subsequent modulation type, via an RF channel,to a transmitter. The receiver may also configure to receive subsequentdata based on the selected current modulation type and/or at least onesubsequent selected modulation type. The receiver may encode aconstellation field to uniquely identify a combination comprising theselected current modulation type, and at least one subsequent selectedmodulation type. The number of constellation points comprised in asubsequent selected modulation type may be less than or equal to thenumber of constellation points comprised in a selected currentmodulation type.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for communicating information in a communications system,the method comprising: in a multiple-input-multiple-output (MIMO)communication system utilizing a plurality of modulation types and aplurality of spatial streams, determining an aggregate noisecharacteristic based upon a noise characteristic of each of saidplurality of spatial streams; and configuring a receiver to receivesubsequent data based on one or both of: a current modulation type formodulating a current spatial stream and at least one subsequentmodulation type for modulating at least one subsequent spatial stream,wherein said current modulation type and said at least one subsequentmodulation type are based on said determined aggregate noisecharacteristic.
 2. The method according to claim 1, comprising encodinga constellation field to uniquely identify a combination comprising saidcurrent modulation type, and said at least one subsequent modulationtype.
 3. The method according to claim 1, wherein said at least onesubsequent modulation type comprises a number of constellation pointsthat is less than or equal to a number of constellation points in saidcurrent modulation type.
 4. The method according to claim 1, comprisingselecting one or both of: said current modulation type and said at leastone subsequent modulation type, based on said determined aggregate noisecharacteristic.
 5. The method according to claim 1, wherein saiddetermined aggregate noise characteristic comprises at least onesignal-to-noise ratio (SNR).
 6. A system for communicating informationin a communications system, the system comprising: circuitry for use ina multiple-input-multiple-output (MIMO) communication system utilizing aplurality of modulation types and a plurality of spatial streams, saidcircuitry operable to determine an aggregate noise characteristic basedupon a noise characteristic of each of said plurality of spatialstreams; and said circuitry operable to configure a receiver to receivesubsequent data based on one or both of: a current modulation type formodulating a current spatial stream and at least one subsequentmodulation type for modulating at least one subsequent spatial stream,wherein said current modulation type and said at least one subsequentmodulation type are based on said determined aggregate noisecharacteristic.
 7. The system according to claim 6, wherein saidcircuitry is operable to encode a constellation field to uniquelyidentify a combination comprising said current modulation type, and saidat least one subsequent modulation type.
 8. The system according toclaim 6, wherein said at least one subsequent modulation type comprisesa number of constellation points that is less than or equal to a numberof constellation points in said current modulation type.
 9. The systemaccording to claim 6, wherein said circuitry is operable to select oneor both of: said current modulation type and said at least onesubsequent modulation type, based on said determined aggregate noisecharacteristic.
 10. The system according to claim 6, wherein saiddetermined aggregate noise characteristic comprises at least onesignal-to-noise ratio (SNR).
 11. A method for communicating informationin a communications system, the method comprising: in amultiple-input-multiple-output (MIMO) communication system utilizing aplurality of modulation types and a plurality of spatial streams,determining an aggregate noise characteristic based upon a noisecharacteristic of each of said plurality of spatial streams; andconfiguring a transmitter to transmit subsequent data based on one orboth of: a current modulation type for modulating a current spatialstream and at least one subsequent modulation type for modulating atleast one subsequent spatial stream, wherein said current modulationtype and said at least one subsequent modulation type are based on saiddetermined aggregate noise characteristic.
 12. The method according toclaim 11, comprising encoding a constellation field to uniquely identifya combination comprising said current modulation type, and said at leastone subsequent modulation type.
 13. The method according to claim 11,wherein said at least one subsequent modulation type comprises a numberof constellation points that is less than or equal to a number ofconstellation points in said current modulation type.
 14. The methodaccording to claim 11, comprising selecting one or both of: said currentmodulation type and said at least one subsequent modulation type, basedon said determined aggregate noise characteristic.
 15. The methodaccording to claim 11, wherein said determined aggregate noisecharacteristic comprises at least one signal-to-noise ratio (SNR).
 16. Asystem for communicating information in a communications system, thesystem comprising: circuitry for use in a multiple-input-multiple-output(MIMO) communication system utilizing a plurality of modulation typesand a plurality of spatial streams, said circuitry operable to determinean aggregate noise characteristic based upon a noise characteristic ofeach of said plurality of spatial streams; and said circuitry operableto configure a transmitter to transmit subsequent data based on one orboth of: a current modulation type for modulating a current spatialstream and at least one subsequent modulation type for modulating atleast one subsequent spatial stream, wherein said current modulationtype and said at least one subsequent modulation type are based on saiddetermined aggregate noise characteristic.
 17. The system according toclaim 16, wherein said circuitry is operable to encode a constellationfield to uniquely identify a combination comprising said currentmodulation type, and said at least one subsequent modulation type. 18.The system according to claim 16, wherein said at least one subsequentmodulation type comprises a number of constellation points that is lessthan or equal to a number of constellation points in said currentmodulation type.
 19. The system according to claim 16, wherein saidcircuitry is operable to select one or both of: said current modulationtype and said at least one subsequent modulation type, based on saiddetermined aggregate noise characteristic.
 20. The system according toclaim 16, wherein said determined aggregate noise characteristiccomprises at least one signal-to-noise ratio (SNR).
 21. A method forcommunicating information in a communications system, the methodcomprising: in a multiple-input-multiple-output (MIMO) communicationsystem utilizing a plurality of modulation types and a plurality ofspatial streams, determining an aggregate power characteristic basedupon a power characteristic of each of said plurality of spatialstreams; and configuring a receiver to receive subsequent data based onone or both of: a current modulation type for modulating a currentspatial stream and at least one subsequent modulation type formodulating at least one subsequent spatial stream, wherein said currentmodulation type and said at least one subsequent modulation type arebased on said determined aggregate power characteristic.
 22. The methodaccording to claim 21, comprising encoding a constellation field touniquely identify a combination comprising said current modulation type,and said at least one subsequent modulation type.
 23. The methodaccording to claim 21, wherein said at least one subsequent modulationtype comprises a number of constellation points that is less than orequal to a number of constellation points in said current modulationtype.
 24. The method according to claim 21, comprising selecting one orboth of: said current modulation type and said at least one subsequentmodulation type, based on said determined aggregate powercharacteristic.
 25. A system for communicating information in acommunications system, the system comprising: circuitry for use in amultiple-input-multiple-output (MIMO) communication system utilizing aplurality of modulation types and a plurality of spatial streams, saidcircuitry operable to determine an aggregate power characteristic basedupon a power characteristic of each of said plurality of spatialstreams; and said circuitry operable to configure a receiver to receivesubsequent data based on one or both of: a current modulation type formodulating a current spatial stream and at least one subsequentmodulation type for modulating at least one subsequent spatial stream,wherein said current modulation type and said at least one subsequentmodulation type are based on said determined aggregate powercharacteristic.
 26. The system according to claim 25, wherein saidcircuitry is operable to encode a constellation field to uniquelyidentify a combination comprising said current modulation type, and saidat least one subsequent modulation type.
 27. The system according toclaim 25, wherein said at least one subsequent modulation type comprisesa number of constellation points that is less than or equal to a numberof constellation points in said current modulation type.
 28. The systemaccording to claim 25, wherein said circuitry is operable to select oneor both of: said current modulation type and said at least onesubsequent modulation type, based on said determined aggregate powercharacteristic.
 29. A method for communicating information in acommunications system, the method comprising: in amultiple-input-multiple-output (MIMO) communication system utilizing aplurality of modulation types and a plurality of spatial streams,determining an aggregate power characteristic based upon a powercharacteristic of each of said plurality of spatial streams; andconfiguring a transmitter to transmit subsequent data based on one orboth of: a current modulation type for modulating a current spatialstream and at least one subsequent modulation type for modulating atleast one subsequent spatial stream, wherein said current modulationtype and said at least one subsequent modulation type are based on saiddetermined aggregate power characteristic.
 30. The method according toclaim 29, comprising encoding a constellation field to uniquely identifya combination comprising said current modulation type, and said at leastone subsequent modulation type.
 31. The method according to claim 29,wherein said at least one subsequent modulation type comprises a numberof constellation points that is less than or equal to a number ofconstellation points in said current modulation type.
 32. The methodaccording to claim 29, comprising selecting one or both of: said currentmodulation type and said at least one subsequent modulation type, basedon said determined aggregate power characteristic.
 33. A system forcommunicating information in a communications system, the systemcomprising: circuitry for use in a multiple-input-multiple-output (MIMO)communication system utilizing a plurality of modulation types and aplurality of spatial streams, said circuitry operable to determine anaggregate power characteristic based upon a power characteristic of eachof said plurality of spatial streams; and said circuitry operable toconfigure a transmitter to transmit subsequent data based on one or bothof: a current modulation type for modulating a current spatial streamand at least one subsequent modulation type for modulating at least onesubsequent spatial stream, wherein said current modulation type and saidat least one subsequent modulation type are based on said determinedaggregate power characteristic.
 34. The system according to claim 33,wherein said circuitry is operable to encode a constellation field touniquely identify a combination comprising said current modulation type,and said at least one subsequent modulation type.
 35. The systemaccording to claim 33, wherein said at least one subsequent modulationtype comprises a number of constellation points that is less than orequal to a number of constellation points in said current modulationtype.
 36. The system according to claim 33, wherein said circuitry isoperable to select one or both of: said current modulation type and saidat least one subsequent modulation type, based on said determinedaggregate power characteristic.